The present invention concerns a gear pump comprising a pump body closed by a cover forming a cavity in which is located a driving pinion capable of being driven in rotation by a driving shaft to which it is fixed, a driven pinion whose teeth cooperate with the teeth of the driving pinion so as to be driven in rotation by the driving pinion, and two flanges located on both sides of the driven pinion protruding into a cavity provided therefor in the pump body and the cover respectively, means being provided for applying a pressure to the external face of the flanges.
Such pumps are often used, in particular as oil, gas, or diesel oil pumps. Their major drawback is that the cover is susceptible to deform under the pressure existing in the discharge zone, which causes an axial play of the loose pinion. The deformation of the cover causes a leakage zone between the discharge and aspiration, so that the volume output of the pump is lowered.
Numerous documents (FR 1 239 211 A, U.S. Pat. No. 3,046,902 A, DE 11 72 959 B, GB 661 772 A, and GB 1 067 552 A) have proposed to dispose between the pinions and the casing four sliding sleeves equipped with recesses for the pinion axes. A function of these sleeves is to make the pump leak-tight by supporting the pinions. To this effect, the external faces of the sleeves are subjected to a determined pressure. In the first document, the external faces are subjected to the entry pressure of the pump, so that the risk of a reflux between the lateral faces of the pinions and the sleeves is not excluded, since the pressure existing in the discharge zone is higher than the pressure exerted on the sleeves. In the four other documents, the external faces are subjected at least in part to the exit pressure. These sleeves have a circular shape corresponding approximately to the diameter of the pinions with a flat area corresponding to the median plane between the two pinions. These sleeves are thus blocked in rotation. Further, the flat areas arranged by pairs form a junction in the area of the median plane between the two pinions, at the location where the risk of backflow is the most important.
These pumps are complicated and require a precise adjusting of the various parts, which makes them costly and fragile.